The present invention relates to golf balls and is more particularly concerned with a new and improved solid golf ball comprising both a multilayer core and a multilayer cover. In particular, one preferred embodiment of the present invention relates to golf balls utilizing double cover layer assemblies in combination with dual and triple layer cores. The cover and core assemblies are selected to provide a particular combination of properties for the resulting golf balls. The invention also provides an embodiment utilizing a metal or metal filled center. The present invention golf balls are generally free from density reducing filler materials and exhibit relatively low moments of rotational inertia.
Golf balls traditionally have been categorized in three different groups, namely, as one piece balls, multi-piece (two or more pieces) solid balls, and wound (three piece) balls. The one piece ball typically is formed from a solid mass of moldable material which has been cured to develop the necessary degree of hardness. It possesses no significant difference in composition between the interior and exterior of the ball. These balls do not have an enclosing cover. One piece balls are described, for example, in U.S. Pat. No. 5 3,313,545; U.S. Pat. No. 3,373,123 and U.S. Pat. No. 3,384,612.
The wound ball is frequently referred to as a three piece ball since it is made with a vulcanized rubber thread wound under tension around a solid or semisolid core and thereafter enclosed in a single or multilayer covering of tough protective material. For many years the wound ball satisfied the standards of the U.S.G.A. and was desired by many skilled, low handicap
One type of three piece wound ball typically has a balata cover which is relatively soft and flexible. Upon impact, it compresses against the surface of the club producing high spin. Consequently, the soft and flexible balata covers along with the wound cores provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade or a backspin which causes the ball to xe2x80x9cbitexe2x80x9d or stop abruptly on contact with the green. Moreover, the soft balata cover produces a soft xe2x80x9cfeelxe2x80x9d to the low handicap player. Such playability properties of workability, feel, etc. are particularly important in short iron play with low swing speeds and are exploited significantly by relatively skilled players.
However, a three piece wound ball also has several disadvantages. For example, a wound ball is difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity, rebound, xe2x80x9cclickxe2x80x9d, xe2x80x9cfeelxe2x80x9d, and the like.
Additionally, a soft wound (three piece) ball is not well suited for use by the less skilled and/or high handicap golfer who cannot intentionally control the spin of the ball. The unintentional application of side spin by a less skilled golfer produces hooking or slicing. The side spin reduces the golfer""s control over the ball as well as reducing travel distance.
Similarly, all the benefits of balata, balata covered balls are easily cut and/or damaged if mishit. Golf balls produced with balata or balata containing cover compositions, therefore, have a relatively short life span. As a result of this negative property, balata and its synthetic substitute, trans polyisoprene, and resin blends, have been essentially replaced as the cover materials of choice by new cover materials comprising ionomeric resins.
Conventional multi-piece solid golf balls, on the other hand, include a solid resilient core having single or multiple cover layers employing different types of material molded on the core. The one piece golf ball and the solid core for a multi-piece solid (nonwound) ball frequently are formed from a combination of materials such as polybutadiene and other rubbers cross linked with zinc diacrylate or zinc dimethacrylate, and containing fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. For multi-piece nonwound golf balls, the cover typically contains a substantial quantity of ionomeric resins that impart toughness and cut resistance to the covers.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of a unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer, resulting in a thermoplastic elastomer exhibiting enhanced properties, such as durability, for golf ball cover construction. However, some of the advantages gained in increased durability have been offset to some degree by decreases in playability. This is because, although the ionomeric resins are very durable, they also tend to be quite hard when utilized for golf ball cover construction and thus lack the degree of softness required to impart the spin necessary to control the ball in flight. Since most ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionic resins lack the xe2x80x9cfeelxe2x80x9d characteristic associated with the softer balata related covers.
As a result, while there are currently more than 50 commercial grades of ionomers available, both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal ions, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients, such as reinforcement agents, etc., a great deal of research continues in order to develop a golf ball cover composition exhibiting not only the improved impact resistance and carrying distance properties produced by the xe2x80x9chardxe2x80x9d ionomeric resins, but also the playability (i.e. xe2x80x9cspinxe2x80x9d, xe2x80x9cfeelxe2x80x9d, etc.) characteristics previously associated with the xe2x80x9csoftxe2x80x9d balata covers, properties which are still desired by the more skilled golfer.
Consequently, a number of multi-piece solid balls have been produced to address these needs. The different types of material used to formulate the cores, covers, etc. of these balls dramatically alter the balls overall characteristics. Various structures have been suggested using multilayer cores and single layer covers wherein the core layers have different physical characteristics. For example, U.S. Pat. Nos. 4,714,253; 4,863,167 and 5,184,828 relate to three piece solid golf balls having improved rebound characteristics in order to increase flight distance. The ""253 patent is directed towards differences in the hardness of the different layers. The ""167 patent relates to a golf ball having a center portion and an outer layer containing a gravity filler such as tungsten or tungsten carbide so as to impart a higher specific gravity to the outer layer than that of the inner layer. Preferably, the outer layer is harder than the center portion. The ""828 patent suggests that the maximum hardness must be located at the interface between the core and the mantle, and the hardness must then decrease both inwardly and outwardly.
A number of patents suggest improving the spin and feel by manipulating the core construction. For example, U.S. Pat. No. 4,625,964 relates to a solid golf ball having a core diameter not more than 32 mm, and an outer layer having a specific gravity lower than that of the core. In U.S. Pat. No. 4,650,193, it is suggested that a curable core elastomer be treated with a cure altering agent to soften an outer layer of the core. U.S. Pat. No. 5,002,281 is directed towards a three piece solid golf ball which has an inner core having a gravity greater than 1.0, but less than or equal to that of the outer shell which must be less than 1.3. U.S. Pat. Nos. 4,848,707 and 5,072,944 disclose three-piece solid golf balls having center and outer layers of different hardness. Other examples of such dual layer cores can be found in, but are not limited to, the followings patents: U.S. Pat. No. 4,781,383; U.S. Pat. No. 4,858,924; U.S. Pat. No. 5,002,281; U.S. Pat. No. 5,048,838; U.S. Pat. No. 5,104,126; U.S. Pat. No. 5,273,286; U.S. Pat. No. 5,482,285 and U.S. Pat. No. 5,490,674. All of these are directed to balls with single cover layers.
Multilayer covers containing one or more ionic resins have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired. This was addressed in U.S. Pat. No. 4,431,193, where a multilayered golf ball cover is described as having been produced by initially molding a first cover layer on a spherical core and then adding a second cover layer. The first or inner layer is comprised of a hard, high flexural modulus resinous material to provide a gain in coefficient of restitution while the outer layer is a comparatively soft, low flexural modulus resinous material to provide spin and control. The increase in the coefficient of restitution provides a ball which serves to attain or approach the maximum initial velocity limit of 255 feet per second, as provided by the United States Golf Association (U.S.G.A.) rules. The relatively soft, low flexural modulus outer layer provides for an advantageous xe2x80x9cfeelxe2x80x9d and playing characteristics of a balata covered golf ball.
In various attempts to produce a durable, high spin ionomeric golf ball, the golfing industry has blended the hard ionomer resins with a number of softer ionomer resins. U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. The hard copolymers typically are made from an olefin and an unsaturated carboxylic acid. The soft copolymers are generally made from an olefin, an unsaturated carboxylic acid and an acrylate ester. It has been found that golf ball covers formed from hard-soft ionomer blends tend to become scuffed more readily than covers made of hard ionomer alone.
Most professional golfers and good amateur golfers desire a golf ball that provides distance when hit off a driver, control and stopping ability on full iron shots, and high spin for short xe2x80x9ctouch and feelxe2x80x9d shots. Many conventional two piece and thread wound performance golf balls have undesirable high spin rates on full shots. The excessive spin on full shots is a sacrifice made in order to achieve more spin on the shorter touch shots. Consequently, it would be desirable to produce a multi-piece golf ball that exhibited low spin on full iron and wood shots and high spin in the xe2x80x9ctouchxe2x80x9d and xe2x80x9cfeelxe2x80x9d shots which occur with the high lofted iron and wedges around the green.
In this regard, the multi-piece nonwound balls, while having an advantage with respect to cut resistance, typically have a cover that is sufficiently hard so as to provide low deformation upon impact and a small contact area between the ball and the club face. This provides a greater degree of slipperiness on the club face and, therefore, less control over the ball and greater difficulty in stopping the ball on the green when using short irons. At least some of these deficiencies are considered to result also from a large moment of inertia exhibited by the multi-piece balls. Thus, it would be useful to develop a ball with a controlled moment of inertia coupled with a soft cover layer in order to provide the desired backspin when using short irons, but at the same time without adversely impacting the desired flight and roll distance of the ball when using a driver.
A dual core, dual cover ball is described in U.S. Pat. No. 4,919,434. However, the patent emphasizes the hardness characteristics of all layers, particularly the requirement for a soft inner cover layer and a hard outer cover layer. With respect to the core, it requires that the layers should not differ in hardness by more than 10 percent and should be elastomeric materials having a specific deformation range under a constant load.
U.S. Pat. No. 5,104,126 attempts to concentrate the weight of the golf ball in the center core region by utilizing a metal ball as the core component. However, that patent teaches the use of density reducing filler materials incorporated elsewhere in the golf ball. Although perhaps satisfactory in some respects, it is undesirable to add density reducing fillers to offset the weight of the center core component. It would be desirable to simply avoid the use of density reducing fillers as they tend to lower the resilience of the golf ball.
Accordingly, it is a feature of the present invention to provide a multi-piece nonwound solid core golf ball where the core has a multilayer construction and the characteristics of both layers of the core are such that the moment of inertia may be adjusted to either enhance or decrease backspin of the ball when using short irons.
Another feature of the invention is to provide a ball having the multilayer core enclosed by a multilayer cover with an appropriate cover hardness and core moment of inertia that will permit extended flight distance of the ball and good roll when using a driver, coupled with a cover having sufficient softness that will permit deformation of the ball upon impact, thereby increasing the contact area between the ball and the club face without subjecting the cover to undesirable cutting or abrasion.
Another feature of the present invention is the provision of a golf ball of the type described that comprises both multilayer cores and multilayer covers in such a manner as to incorporate the desirable features associated with various categories of balls traditionally employed.
A further feature of the present invention is the provision for a golf ball core structure with an inner or center core and an outer core layer, with the inner core having a specific gravity that differs from that of the outer core layer, thereby giving the golf ball a moment of inertia differing from that of typical solid core balls.
Yet another feature is the provision for a multilayer core that is combined with a multilayer cover wherein the outer cover layer has a lower hardness value than the inner cover layer.
A further feature is the provision for a golf ball having a soft outer cover layer with good scuff resistance and cut resistance coupled with relatively high spin rates at low club head speeds.
The present invention provides in the first aspect, a solid, nonwound golf ball free of density reducing filler materials, and comprising a multi-core assembly that is concentrically positioned within the center of the golf ball, and a multi-layer cover assembly disposed about the multi-core assembly. The mass and position of both the multi-core assembly and the multi-layer cover assembly are such that the moment of inertia of the golf ball is less than 0.43 oz. in2 for a 1.680xe2x80x3 golf ball.
In yet another aspect, the present invention provides a golf ball comprising a center core component which is concentrically disposed about a reference point located at the geometric center of the golf ball. The golf ball further comprises a core layer which generally surrounds and is disposed about the center core component. The golf ball further comprises a first inner cover layer disposed and positioned around the core layer, and a second outermost dimpled cover layer that is disposed about the first inner cover layer. An ionomeric material is used in at least one of the cover layers. The configuration of the golf ball is such that it has a moment of inertia of less than 0.43 oz. in2 for a 1.680xe2x80x3 golf ball.
In yet another aspect, the present invention provides a golf ball comprising a center core component having a specific gravity in the range of from about 1.0 to about 20, and a diameter in the range from about 3 mm to about 20 mm. The golf ball further comprises a core layer disposed about the center core component, the core layer having a specific gravity in the range from about 0.9 to about 1.2, and an outer diameter in the range from about 30 mm to about 40 mm. The golf ball further includes an inner cover layer disposed about the core layer, and an outer cover layer disposed about the inner cover layer. The golf ball exhibits a moment of inertia less than 0.43 oz. in2, and a coefficient of restitution of at least 0.760. The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth.